The present invention is directed, in general, to geophysical exploration and, more specifically, to a system and method for orienting seismic energy sources and receivers to yield discriminated horizontal and vertical shear waves.
Currently, most geophysical techniques dealing with multi-dimensional seismic data do not discriminate or locate seismic energies of different orientations, such as the horizontal shear energy and the vertical shear energy portions of directed seismic energy. In a typical multi-dimensional seismic survey, a multi-mode seismic energy generator may be used to generate a preponderance of one orientation of seismic energy relative to a particular orientation, then a preponderance of energies orthogonal to the first, relative to the same orientation. However, the orientation of the received seismic energies changes at each receiver due to the fact that the orientation between the seismic energy source and each receiver in a multi-dimensional seismic array is different.
Differently oriented seismic energies travel differently through the subsurface strata based upon the characteristics of the subsurface strata. Thus, if a fault plane in the strata were in more of a vertical orientation relative to the plane defined by the seismic energy source-receiver line, the different seismic energies would have a different travel characteristic. The mapping of the subsurface features could be greatly enhanced through processing of these oriented seismic energies, especially in an orientation specific to the azimuths defined by each receiver with the seismic energy source. Additionally, important rock property information can be ascertained by comparing differences and similarities of the attributes of the oriented seismic energies.
However, the processing of such data is complicated, because the oriented energies are not easily discriminated into the differently oriented energies for each receiver-source azimuth. Also, the processing of these components is complicated since the orientation of the operational modes of the seismic energy source do not always correspond to the orientation of each and every receiver in the geophysical array. Many other problems and disadvantages of the prior art will be become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.
To address the above-discussed deficiencies of the prior art, the present invention provides a system for, and method of, orienting seismic energy sources and seismic energy receivers to yield discriminated horizontal and vertical shear modes. In one embodiment, the system includes: (1) an initial matrix representing wave energy produced by a selected seismic energy source and received by a selected seismic energy receiver, (2) a first transforming matrix that cooperates with the initial matrix to orient the selected seismic energy source with respect to the selected seismic energy receiver and (3) a second transforming matrix that cooperates with the initial matrix to orient the selected seismic energy receiver with respect to the selected seismic energy source, the initial matrix thereby transformed into a successive matrix containing the discriminated horizontal and vertical shear modes.
In one embodiment of the present invention, the wave energy is expressed in the initial matrix as inline and crossline components. In a related embodiment of the present invention, the first and second transforming matrices are a function of locations of the seismic energy sources and seismic energy receivers. In another embodiment of the present invention, the wave energy is recorded. And in yet another embodiment of the present invention, a volumetric image of subsurface formations is determined as a function of the discriminated horizontal and vertical shear modes.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.